Vegetable oil fuels – mutagenicity of exhaust particles of conventional and new types of fuels
Besides petroleum-based fuels (petrol, diesel), use of biomass-based fuels is increasing: Whereas the share of renewable energy sources in Germany still only accounted for 0.4 % of fuel use in 2000, in 2008 it had already reached 6.1 %. Around 2.8 million mg biodiesel, 0.42 million mg vegetable oil, 0.63 million mg bioethanol and small quantities of (treated) biogas were burned.
Reports issued by a workgroup questioned the continued use of biofuels, especially vegetable oils: The authors had observed highly increased values of exhaust particle mutagenicity in vegetable oil burning.
Vegetable oil fuels in the test
Therefore, on behalf of a diesel engine manufacturer, an engine conversion firm, users of vehicles run on vegetable oil as well as the technology and development centre TFZ Straubing (Technologie- und Förderzentrum im Kompetenzzentrum für Nachwachsende Rohstoffe), bifa investigated the mutagenicity of exhaust particles produced by vegetable oil and diesel. In these investigations the exhaust, diluted with air and cooled to temperatures below 52 °C, was tested in engine test stands in accordance with internationally valid test regulations. The exhaust particles were separated out onto filters. The soot constituents were then extracted in the laboratory and examined for mutagenic (genetically modifying) effects in the Ames test.
In this biotest the extract constituents affect the genetic make-up of bacteria: In mutagenic substances are present the number of so-called revertants increases sharply. These are bacteria which can grow without the addition of certain nutrients. The number of bacterial colonies of these revertants provides information about the mutagenic potential of a test sample. While potent mutagenic substances such as 3-NBA have a mutagenic effect at doses of 0.0000000001 mg and higher, a billion (109) times more diesel or vegetable oil soot is required before its constituent quantities have a comparable mutagenic effect.
No increased levels of mutagenic constituents
The tests carried out by bifa all consistently showed that the sampled exhaust particles produced by vegetable oil burning do not contain any increased levels of mutagenic constituents compared to the exhaust particles of diesel combustion.
These results have now been confirmed in tests carried out by numerous other workgroups.
Nevertheless, one workgroup repeatedly reports results to the contrary: It reports that when biofuels are used, exhausts with increased mutagenicity occur if altered sampling conditions are used (undiluted exhaust; sampling of stationary and transient (steady and unsteady) operating phases). However, it is currently still unclear whether the mutagenic compounds found by this group actually existed in the exhaust or were formed during sampling and were then false positive findings.